1. Field of the Invention
The present invention relates to an antenna apparatus, and more particularly, to an antenna apparatus including an electromagnetic shielding box.
2. Description of the Related Art
In a wireless communication system, an antenna apparatus is needed to transmit and receive electromagnetic wave carrying signals. Dipole antenna architecture is one of the basic antenna architectures and originated from an invention in the 19th century. FIG. 1 shows the architecture of a dipole antenna. As shown in FIG. 1, the dipole antenna 100 comprises two antenna ends extending outward from a feed point. A first antenna end 104 serves as a signal source of the dipole antenna 100. A second antenna end 106 serves as a ground of the dipole antenna 100. The current directions of the first antenna end 104 and the second antenna end 106 are shown in FIG. 1, wherein the current level reaches the highest level at the feed point, and reaches zero at the ends of the first antenna end 104 and the second antenna end 106. There are many examples of the application of the dipole antenna. One example is the early TV antenna design.
The following introduces the architecture of monopole antenna, another basic antenna architecture, which is derived from the dipole antenna architecture. FIG. 2 shows the architecture of a monopole antenna. The monopole antenna 200 comprises one antenna end 204 extending outward from a feed point. The antenna end 204 is perpendicular to a ground plane. As shown in FIG. 2, the ground plane replaces the second antenna end 106 of the dipole antenna 100. Accordingly, the antenna end 204 serves as a signal source of the monopole antenna 200, and the ground plane serves as the ground of the monopole antenna 200. The current directions of the antenna end 204 and the ground plane are shown in FIG. 2, wherein the current of the ground plane is scattered from the feed point to the vicinity thereof. Examples of the application of monopole antennas include radio masts and towers.
For small wireless communication apparatuses, such as a wireless communication apparatus in a universal serial bus (USB) application, both dipole antenna and monopole antenna designs may serve as the antenna apparatus of the wireless communication apparatus. FIG. 3 shows a side view of a conventional monopole antenna in a USB application. As shown in FIG. 3, the monopole antenna 300 comprises a printed circuit board 302, an antenna end 304 and an electromagnetic shielding box 306. The printed circuit board 302 comprises a radio frequency circuit of the monopole antenna 300. The antenna end 304 comprises a metal antenna and is connected to the printed circuit board 302. The electromagnetic shielding box 306 covers the printed circuit board 302 to provide noise suppression for the monopole antenna 300.
FIG. 4 shows a schematic view of the monopole antenna 300 shown in FIG. 3. As shown in FIG. 4, the antenna end 304 serves as a signal source of the monopole antenna 300, and the electromagnetic shielding box 306 serves as a ground of the monopole antenna 300.
Conventional monopole antennas in a USB application inherit disadvantages of typical monopole antennas. For example, compared to dipole antennas, monopole antennas exhibit lower input impedance. In addition, dipole antennas have higher radiation resistance than monopole antennas, and accordingly are more efficient than monopole antennas. On the other hand, small wireless communication apparatuses using dipole antennas may not meet consumer requirements since dipole antennas require much greater size.
Therefore, there is a need for an antenna apparatus that exhibits both small size and high efficiency, combining advantages of monopole and dipole antenna designs. The present invention provides such antenna apparatus.